1. Cross-Reference to Related Applications
This application is related to the co-pending application of Danny Eugene Scott and Stephen R. Jurewicz entitled IMPROVED ROCK BIT COMPACT AND METHOD OF MANUFACTURE and to the co-pending application of Stephen R. Jurewicz and Danny Eugene Scott entitled ROTARY ROCK BIT WITH IMPROVED DIAMOND FILLED COMPACTS, filed concurrently herewith.
2. Field of the Invention
The present invention relates generally to earth boring bits of the fixed cutter type and to improvements in compacts used in the cutting structures thereof, the improved compacts being formed with a hard metal jacket and an integrally formed, diamond filled core.
3. Description of the Prior Art
Wear resistant inserts or compacts are utilized in a variety of earth boring tools where the inserts form rock cutting, crushing, chipping or abrading elements. In rotary well drilling, some geological formations are drilled with bits having cutting structures of wear resistant (usually sintered tungsten carbide) compacts held in receiving apertures in rotatable cones. In such bits, there is usually on each cone a group of cylindrical compacts that define a circumferential heel row that removes earth at the corner of the bore hole bottom. Further, it is common to insert additional cylindrical compacts, called "gage" compacts, on a "gage" surface that intersects a generally conical surface that receives the heel row compacts. These gage compacts protect the gage surfaces to prevent erosion of the metal of the cones that supports the heel row compacts. As a result, fewer heel compacts are lost during drilling and the original diameter of the bit is better maintained due to decreased wear. Moreover, the gage compacts also ream the hole to full "gage" after the heel compacts are worn to an undersized condition.
Fixed cutter bits, either steel bodied or matrix, are also utilized in drilling certain types of geological formations effectively. While these bits do not feature rotatable cones, they also have wear resistant inserts advantageously positioned in the "shoulder" or "gage" regions on the face of the bit which are essential to prolong the useful life of the bit.
A typical prior art wear resistant insert was manufactured of sintered tungsten carbide, a composition of mono and/or ditungsten carbide cemented with a binder typically selected from the iron group, consisting of cobalt, nickel or iron. Cobalt generally ranged from about 10 to 16% of the binder, the balance being tungsten carbide. The exact composition depended upon the usage intended for the tool and its inserts.
In recent years, both natural and synthetic diamonds have been used, in addition to tungsten carbide compacts, as cutting inserts on rotary and fixed cutter rock bits. In fact, it has long been recognized that tungsten carbide as a matrix for diamonds has the advantage that the carbide itself is wear resistant and offers prolonged matrix life. U.S. Pat. No. 1,939,991 to Krusell describes a diamond cutting tool utilizing inserts formed of diamonds held in a medium such as tungsten carbide mixed with a binder of iron, cobalt, or nickel.
In some prior art cutting tools, the diamond component of the tool was formed by the conversion of graphite to diamond. U.S. Pat. No. 3,850,053 describes a technique for making cutting tool blanks by placing a graphite disk in contact with a cemented tungsten carbide cylinder and exposing both simultaneously to diamond forming temperatures and pressures. U.S. Pat. No. 4,259,090 describes a technique for making a cylindrical mass of polycrystalline diamond by loading a mass of graphite into a cup-shaped container made from tungsten carbide and diamond catalyst material. The loaded assembly is then placed in a high temperature and pressure apparatus where the graphite is converted to diamond. U.S. Pat. No. 4,525,178 shows a composite material which includes a mixture of individual diamond crystals and pieces of precemented carbide.
U.S. Pat. No. 4,148,368 shows a tungsten carbide insert for mounting in a rolling cone cutter which includes a diamond insert embedded in a portion of the work surface of the tungsten carbide cutting insert in order to improve the wear resistance thereof. Various other prior art techniques have been attempted in which a natural or synthetic diamond insert was utilized. For instance, there have been attempts in the prior art to press-fit a natural or synthetic diamond within a jacket, with the intention being to engage the jacket containing the diamond within an insert receiving opening provided on the bit face or cone. These attempts were not generally successful since the diamonds tended to fracture or become dislodged in use.
There continues to exist a need for improvements in compacts of the type utilized as wear resistant inserts in fixed cutter earth boring bits, particularly in the gage and shoulder regions thereof, which will improve the useful life of such bits.
A need also exists for improvements in the wear resistant inserts used in such bits, whereby such inserts are provided with improved abrasion resistance and diamond retention characteristics.